It relates to a discussion of possible military operations in Syria, which was apparently attended by Turkey's intelligence chief, its foreign minister and the deputy head of the armed forces.

Reuters news agency, which examined the recording, said it could not verify its authenticity but it was potentially the most damaging purported leak so far as it appeared to have originated from the bugging of a highly confidential and sensitive conversation.

Mr Erdogan, who faces important local elections on Sunday, accuses social media of spreading misinformation and suggested earlier that bans could be applied to both YouTube and Facebook.

'Villainous' leak

In its statement, the TIB said: "After technical analysis and legal consideration.... an administrative measure has been taken for this website."

As conflicting reports emerged over the blockage, the search engine Google, which owns YouTube, confirmed that some users were unable to access YouTube in Turkey.

"There is no technical issue on our side and we're looking into the situation," a Google Inc spokesperson said in a statement to Reuters.

The term #youtubeblockedinturkey has begun trending worldwide on Twitter.

At a rally in the south-eastern city of Diyarbakir on Thursday, Mr Erdogan appeared to confirm the latest audio leak was genuine.

"They even leaked a national security meeting," he said. "This is villainous, this is dishonesty... Who are you serving by doing audio surveillance of such an important meeting?"

On Wednesday, a court in the capital, Ankara, ordered the TIB to lift its ban on Twitter, but it could be weeks before the order takes effect.

Twitter itself has filed a challenge to the access ban. It said it was concerned about a court order to suspend an account which had accused a former minister of corruption.